Ethanol for industrial use is conventionally produced from petrochemical feed stocks, such as oil, natural gas, or coal, from feed stock intermediates, such as syngas, or from starchy materials or cellulose materials, such as corn or sugar cane. Conventional methods for producing ethanol from petrochemical feed stocks, as well as from cellulose materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Instability in petrochemical feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. Starchy materials, as well as cellulose material, are converted to ethanol by fermentation. However, fermentation is typically used for consumer production of ethanol, which is suitable for fuels or human consumption. In addition, fermentation of starchy or cellulose materials competes with food sources and places restraints on the amount of ethanol that can be produced for industrial use.
Ethanol production via the reduction of alkanoic acids and/or other carbonyl group-containing compounds has been widely studied, and a variety of combinations of catalysts, supports, and operating conditions have been mentioned in the literature. During the reduction of alkanoic acid, e.g., acetic acid, other compounds are often formed with ethanol or are formed in side reactions. For example, during hydrogenation, esters are produced that together with ethanol and/or water form azeotropes, which are difficult to separate. These impurities may limit the production of ethanol and may require expensive and complex purification trains to separate the impurities from the ethanol. Also, the hydrogenation of acetic acid typically yields ethanol and water along with small amounts of side reaction-generated impurities and/or by-products. At maximum theoretical conversion and selectivity, the crude ethanol product would comprise approximately 72 wt. % ethanol and 28 wt. % water. In order to form purified ethanol, much of the water that is co-produced must be removed from the crude ethanol composition. In addition, when conversion is incomplete, unreacted acid may remain in the crude ethanol product. It is typically desirable to remove this residual acetic acid from the crude ethanol product to yield purified ethanol.
EP02060553 describes a process for hydrogenating ethanoic acid to ethanol and for reducing the proportion of ethyl ethanoate by co-feeding water.
The need remains for improving the recovery of ethanol from a crude product obtained by reducing alkanoic acids, such as acetic acid, and/or other carbonyl group-containing compounds.